When we first heard about researchers using tiny freely floating tools to grab tissue samples deep inside the body, we were scared.

But our fears quickly turned to fascination.

Johns Hopkins engineers are testing out what they call "untethered microgrippers" as a better way to investigate hard-to-reach places. They have launched hundreds of these things, which look like miniature ninja throwing stars, inside the body of animal to retrieve tiny pieces of tissue for biopsies.

The microgrippers are as small as a speck of dust. And they work completely on their own — no strings attached, no electricity required.

"It's like a spring-loaded system or latch," bioengineer David Gracias, who developed the devices, tells Shots. "When it reaches the right temperature in the body, the microtool folds up."

And, they're magnetic. So doctors can — in theory – get them all back.

"In the bile duct [of a pig], we could retrieve 95 percent of them," Gracias says. "But there were one or two left behind. That is one of our concerns."

Clearly, the microgrippers aren't ready for use in humans. But Gracias and his team have started testing them out on animals.

In January, the team launched hundreds of them into a pig's bile duct, the tiny channels that connect the liver to the intestine.

Standard forceps for biopsies can't reach these narrow channels because of their size. But the microgrippers easily make the trip.

"We released the tools in the bile duct and then waited 10 minutes," he explains. "The microgrippers move around the tortuous channels, grab pieces of tissue and then we could do standard pathology and genetic analysis on the tissue."

The results aren't comparable to a regular biopsy, Gracias admits, because the samples are much smaller. But the microgrippers can take many more samples, he says, and they aren't as destructive. "It's less invasive, less scarring."

More recently, his team tried out the fleet in a pig's colon — a place where Gracias thinks the microgrippers could really shine.

For some diseases in the gut, tumors can be too small to see, Gracias says. "The common practice is take 30 samples with large biopsies from different regions of the colon," he says. "But the colon is so large, you're sampling only 0.3 percent of it. A better way to is to take many smaller samples."

Besides, leaving a few microgrippers behind isn't such a big problem in the colon, Gracias says. They'd just pass out naturally.

Gracias and his team came up with the idea for the microtools while building nanomachines that automatically fold up into a particular shape, like a box or polyhedron.

He designed the grippers to look like hands. There's a polymer material at the base of each finger, which softens when it warms up. This makes the fingers fold over. Whatever is near them gets grabbed and torn off.

Gracias and his team are just starting to get money for safety tests in people. And they hope to make the devices biodegradable, so they don't have to worry about retrieval.

But still, there's a long way to go before you'll see microgrippers at your next biopsy.

"The big dream in medicine is to build very small tools that could access tiny places in the body in a noninvasive way," he tells Shots. "There are a lot of surgical robots, like toy cars. But typically these robots need batteries — so they are very hard to make small."

"This is a completely new area of surgery and medicine," he says. "There are a lot of challenges, but if they are overcome, biopsies would less invasive, less traumatic. There'd be less scarring. It would be amazing."